1. Field of the Invention
The invention is directed to a method for localizing (identifying) a site of origin of an electrical heart activity. More specifically the invention is directed to such a localization method of the type wherein body surface potentials generated by the heart activity are measured at a number of measuring points with a multi-channel measuring system and values that characterize the body surface potentials at the measuring points are stored. These values are compared to comparison values stored in a databank, the comparison values characterize comparison surface potentials that arise from comparison heart activities whose position in the heart is known, and the position of that comparison heart activity whose comparison values exhibit the most similarity to the characteristic values is emitted as the site of origin of the heart activity in question.
2. Description of the Prior Art
A method of the type generally described above is known from an article by Sippens-Groenewegen et al. entitled, "Localization of the Site of Origin of Postinfarction Ventricular Tachycardia by Endocardial Pace Mapping", Circulation, Volume 88, No. 5, Part 1, November 1993, pp. 2290-2306. Body surface potentials of electrical heart activities are simultaneously taken at the thorax surface with sixty-two electrodes. These signals are integrated over the QRS complex. The integrated measured value, as a characteristic value, is then compared to corresponding comparison values that arise from comparison heart activities originating from a known position. The position of that comparison heart activity whose comparison values agree best with the characteristic values is emitted as the localization result.
Details of how the comparison values of comparison heart activities are generated are set forth in the article by Sippens-Groenewegen et al. entitled, "Body Surface Mapping of Ectopic Left and Right Ventricular Activation, Circulation, Volume 82, No. 3, September 1990, pp. 879-896. According thereto, comparison surface potentials are measured for healthy persons with a multiple electrode arrangement, these comparison surface potentials being generated by a stimulation catheter in the heart. The location of the catheter is determined by means of a biplanar (stereo) cineradiographic method. The compilation of sufficiently large number of comparison heart activities and the associated comparison body surface potentials for the localization is extremely complicated because of the required measurements of both healthy patients and patients exhibiting pathological cardiac activity.
An article by Killmann et al. entitled "Three-dimensional computer model of the entire human heart for simulation of reentry and tachycardia: gap phenomenon and Wolff-Parkinson-White syndrome", Basic Research in Cardiology, Volume 86, 1991, pp. 485-501, discloses a computer model for the simulation of normal and pathological ECG data. In the heart model, the heart is divided into volume cells that are interconnected according to the heart physiology. Electrophysiological parameters are allocated to each cell. In particular, the parameters of conduction velocity refractory period and cycle length are allocated to the cells. These can be freely selected within the scope of physiologically meaningful values. Proceeding from a stimulation at the sinus node, the individual volume cells are subsequently activated in the modelled stimulation propagation in accord with the electrophysiological parameters allocated to them. The stimulation propagation is accompanied by an electrical field from which body surface potentials can be calculated. The cells have a size of about 2.5 mm.
A method for calculating comparison surface potentials is disclosed in the article by Bommel et al., "Boundary Element Solution of Biomagnetic Problems", IEEE Trans. Magn. MAG-29, 1993, pp. 1395-1398. With the assistance of a modified boundary element method, electrical values generated by a heart model am utilized for the calculation of the distribution of body surface potentials on a thorax model.
A method of principal component analysis as disclosed, for example, in the article by Wold et al., "Principal Component Analysis", Chemometrics and Intelligent Laboratory Systems, Volume 2, 1987, pp. 37-52, is known for use in reducing large datasets to their characteristic informational content.
German OS 43 07 545 discloses an apparatus and a method for identifying the location and/or extent of ischemia and/or infarctions in the heart of a subject. Measured ECG values are supplied to a neural network therein. With the assistance of the aforementioned heart model, a neural network is correspondingly trained to emit the location and/or the extent of pathological modifications from the ECG data. The preparatory outlay for realizing a neural network that is suitable for resolving the localization task, however, is high.